at number 647 was sold to an art dealer the next month. According to the Real Estate Record and Guide, these sales marked "another step in the transition of this section of Fifth avenue from the residential to the business stage". In July 1917, Louis J. Cartier and Pierre C. Cartier decided to buy the Plant House outright. The trade consisted of $100 in cash and included a double-stranded necklace of 128 flawlessly matched natural pearls valued at the time at $1 million (equivalent to $ in ). Mae Plant had admired this necklace in the window of Cartier's 712 Fifth Avenue shop. Because of the later advent of cultured pearls causing the prices of pearls to plunge, the Cartier necklace was worth only $151,000 (equivalent to $ in ) after Mae Plant died in 1956. William Welles Bosworth designed a conversion of the Plant House into a Cartier store. As part of the Plant House's conversion, the original front doorway in the middle of the facade on 52nd Street was removed. The Fifth Avenue Association granted its "gold medal for altered buildings" to Cartier in November 1917 for its alteration of the Plant House. Cartier hired Bosworth again in 1919 to make further alterations to the Plant residence. 1920s to 1950s The Cartier store was shared with Charvet & Fils, a gentlemen's haberdasher, until 1927. The store also hosted events such as a 1927 exhibition of old timepieces. Nicholas C. Partos took a 63-year lease on Luce's house in March 1927 and considered erecting a 12-story commercial structure on the site. Louis F. Mentz bought Luce's house that July, including a $200,000 mortgage on the property. The house was resold shortly afterward to the 653 Fifth Avenue Corporation, which owned the former Plant residence that Cartier occupied. It was likely around this time that the two houses were joined internally. In November 1928, an information bureau for the French government opened at 4 East 52nd Street. 4 East 52nd Street came to be occupied by the French Chamber of Commerce and the Alliance Française de New York, which respectively elected Pierre C. Cartier as their president in 1935 and 1938. The French Chamber of Commerce continued to occupy 4 East 52nd Street until at least 1945, when it hosted an exhibit of French craftsmanship. The houses at 653 Fifth Avenue and 4 East 52nd Street, along with the neighboring